Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Discrete semiconductor devices generally contain one type of electrical component, e.g., light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, and power metal oxide semiconductor field effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, microprocessors, charged-coupled devices (CCDs), solar cells, and digital micro-mirror devices (DMDs).
Semiconductor devices perform a wide range of functions such as high-speed calculations, transmitting and receiving electromagnetic signals, controlling electronic devices, transforming sunlight to electricity, and creating visual projections for television displays. Semiconductor devices are found in the fields of entertainment, communications, power conversion, networks, computers, and consumer products. Semiconductor devices are also found in military applications, aviation, automotive, industrial controllers, and office equipment.
Semiconductor devices exploit the electrical properties of semiconductor materials. The atomic structure of semiconductor material allows its electrical conductivity to be manipulated by the application of an electric field or base current or through the process of doping. Doping introduces impurities into the semiconductor material to manipulate and control the conductivity of the semiconductor device.
A semiconductor device contains active and passive electrical structures. Active structures, including bipolar and field effect transistors, control the flow of electrical current. By varying levels of doping and application of an electric field or base current, the transistor either promotes or restricts the flow of electrical current. Passive structures, including resistors, capacitors, and inductors, create a relationship between voltage and current necessary to perform a variety of electrical functions. The passive and active structures are electrically connected to form circuits, which enable the semiconductor device to perform high-speed calculations and other useful functions.
Semiconductor devices are generally manufactured using two complex manufacturing processes, i.e., front-end manufacturing, and back-end manufacturing, each involving potentially hundreds of steps. Front-end manufacturing involves the formation of a plurality of die on the surface of a semiconductor wafer. Each die is typically identical and contains circuits formed by electrically connecting active and passive components. Back-end manufacturing involves singulating individual die from the finished wafer and packaging the die to provide structural support and environmental isolation.
One goal of semiconductor manufacturing is to produce smaller semiconductor devices. Smaller devices typically consume less power, have higher performance, and can be produced more efficiently. In addition, smaller semiconductor devices have a smaller footprint, which is desirable for smaller end products. A smaller die size may be achieved by improvements in the front-end process resulting in die with smaller, higher density active and passive components. Back-end processes may result in semiconductor device packages with a smaller footprint by improvements in electrical interconnection and packaging materials.
In FIG. 1, a conventional flipchip type semiconductor die 10 and wire-bonded semiconductor die 12 are stacked on leadframe 14. The smaller semiconductor die 10 is mounted to leadframe 14 with bumps 16. The larger semiconductor die 12 is stacked over the smaller semiconductor die 10 with die attach adhesive 18. Semiconductor die 12 is electrically connected to leadframe 14 using bond wires 20. An encapsulant 22 is deposited over semiconductor die 10 and 12. The stacked semiconductor die with bump and bond wire interconnects increases the size requirements of the leadframe, which adds to manufacturing costs. The relatively long signal path length for semiconductor die 12, due to bond wires 20, degrades electrical performance. The overhang of the larger semiconductor die 12 can cause a bounce or cantilever effect during the wire-bonding process.
In some cases, flipchip type semiconductor die are mounted to a leadframe in a quad flat no-lead package (QFN). Flipchip die are low cost and provide fast signal propagation due to minimal lead lengths. To mount multiple flip-chip die on the leadframe, the die can be mounted side-by-side, which requires a large leadframe area. To stack the flipchip die vertically, the electrical interconnect between the die becomes problematic. A solder bump interconnect has the limitation of collapsing upon reflow, especially for the large bumps needed for stacked die. In addition, the large bumps also limit input/output (I/O) pitch and I/O pin count.